It is well known that the nerve that should be primarily protected during thyroidectomy is the recurrent laryngeal nerve (RLN). This is because if the RLN is injured during surgery, it may lead to voice disorders such as hoarseness, which can be difficult to recover from. So, if extreme caution is taken during surgery to avoid injuring the RLN, will the aforementioned symptoms still occur?

The answer is no. According to reports, among all patients undergoing thyroidectomy who did not sustain RLN injury during surgery, 80% still experienced changes in their voice.

This raises the question: what other factors contribute to voice disorders after thyroidectomy?

In recent years, James C. Lee and colleagues published a quantitative study in Surgery regarding the factors related to voice disorders after thyroidectomy, concluding that the severity of voice disorders postoperatively is related to the degree of swelling of the RLN during surgery, as well as the extent of thyroid tissue removed during surgery.

This is a prospective clinical study originating from Australia, where researchers screened patients undergoing total or partial thyroidectomy in their hospital over a 12-month period. Patients who had recently undergone lymph node dissection were excluded.

All patients underwent laryngoscopy before and after surgery, primarily to assess vocal cord function and determine whether RLN paralysis occurred postoperatively.

The study focused on voice assessment, which included two aspects: subjective assessment and objective assessment. The former was evaluated using the Voice Disability Index (VDI, or VHI), while the latter used the Degree of Speech Impairment (DSI) for evaluation. Finally, a speech pathologist recorded the scores from both assessments into a scoring system for analysis.

Note: The VDI is a self-assessment scale with a scoring range of 0 to 40, where a higher score indicates poorer voice quality; the DSI is an objective quantitative assessment, with +5 indicating normal, and lower scores indicating more severe voice impairment, with -5 being the worst.

The assessment times included: 6 weeks preoperatively, 1 day postoperatively, and follow-up assessments at 6 to 12 months postoperatively.

All patients underwent thyroidectomy using standard methods, routinely receiving 8 mg of dexamethasone preoperatively, and measuring the RLN diameter twice during surgery using a 0.1 mm caliper (once when the RLN was first identified and once after the thyroid lobe was removed). All patients routinely used neurophysiological monitoring devices to assist with surgery.

A total of 62 patients completed the entire study, with an average age of approximately 48 years, including 53 females and 9 males. 37 (60%) underwent total thyroidectomy, and 25 (40%) underwent partial thyroidectomy. A total of 4 (6.5%) patients experienced RLN paralysis postoperatively. Fortunately, all 4 patients experienced only temporary RLN paralysis, with none developing permanent RLN paralysis.

Overall, the subjective VDI assessments and objective DSI scores of the patients were remarkably similar:

• First, the VDI increased from 4.2 points preoperatively to 9.4 points postoperatively, and the DSI decreased from 3.9 points preoperatively to 2.8 points postoperatively, indicating a significant decline in voice quality after thyroidectomy;

• Secondly, the 4 patients who developed RLN paralysis postoperatively had significantly higher VDI scores than other patients; similarly, their DSI scores were significantly lower than those of other patients.

Subgroup analysis revealed:

• Whether undergoing total or partial thyroidectomy, patients experienced a significant decrease in VDI scores postoperatively, indicating that both surgical methods led to a subjective perception of decreased voice quality.

• However, DSI score results showed that only patients undergoing total thyroidectomy exhibited a significant decline in voice quality postoperatively.

Follow-up results indicated that at 6 to 12 months postoperatively, all patients’ VDI and DSI scores returned to preoperative levels.

Additionally, intraoperative measurements of RLN diameter revealed that all patients experienced significant swelling, with an average diameter increase of approximately 0.58 mm. Further Pearson correlation analysis found that for patients undergoing partial thyroidectomy, the degree of RLN swelling was significantly positively correlated with the severity of voice impairment reflected in their DSI scores, meaning that the more severe the RLN swelling, the lower the DSI score, indicating more severe voice impairment. However, this phenomenon was not observed in patients undergoing total thyroidectomy.

In light of the above results, the authors summarize the following points:

1. Even if the RLN is not injured during surgery and its function is intact, patients may still experience a decline in voice quality after thyroidectomy.

2. The influencing factors are multifaceted; this study suggests that the extent of thyroid tissue removal and the degree of RLN swelling may be related to the severity of voice impairment.

3. Most voice disorders of this type after thyroid surgery can spontaneously recover.

Editor: Cheng Peixun

Editor-in-Chief: Zhou Mengmeng

Image Source: Shutterstock

Submission Email: [email protected]